Duplex carrier-wave transmitting and receiving system



June 1,1926. 1,586,985 H. T. FRHS DUPLEX CARRIER WAVE TRANSMITTING AND RECEIVING SYSTEM Filed Dec. 28, 1921 //7 vniar. Ham/d 277/73:

Patented June 1, 1926.

HARALD TRAP FRTIS", 035' BED B'A'NK, NEW JERSEY, ASSIGNOR TO' \VESHEERN' ELECTRIC COMPANY, INCORPORATEQ'OF NEW YORK} N. Y1, .ACORPO'RATION 0F NEVJ' YORK.

DUPLEX GARRIERJVAVE TRANSMITTING AND RECEIVING SYSTEM.

Application filed"! December This invention relates to duplex. carrier Wave transmitting. and. receiving systems, and more particularly to suchv a. system come prising means permitting, either the transmitting circuit or the receiving circuit, ac,- cording to the particular function to be connected to the common transmitting. and receiving conductor, and et'tectually excluding the other circuit from such connection.

An object of the invention is to provide means for substantially simultaneously rendering the reciving circuit operative, and the transmitting circuit: inoperative, or vice versa, without the use of. a circuit closing means.

A specific object is to utilize the modue lating currents employed in the normal transmitting function to perform. the above stated operations.

An additional object is to accomplish the desired function and to complete the transition Within a brief interval of time, but sufficiently great to prevent accidental opera. tion by brief extraneous impulses which may simulate closely the characteristics of modulating current impulses.

A duplex station as here: understood coinprises the association Witha common conductor, such as an antenna, of the circuits and apparatus characteristic respectively of transmitting and receiving circuits" An essential feature is the provision of means for preventing the outgoing energy in the common conductor from circulating the associated receiving circuits. Such effect is 00111- monly known as side-tone interference. Among the evils attending the presence of the interfering current is the tendency of the system to oscillate and this may be only partially eliminated by the use of selective circuits.

Circuit closing means have been proposed to put either circuit. at wilL in connection with the common conducting means, the ren'iaining circuit being at the same time disconnected therefrom. By this means, however, the desired result is secured at the sacrifice of the convenience afforded by automatic operation, and the scheme is further objectionable on account of sparking at the switch contacts.

According to the present invention the transmitting circuit and receiving, circuit are. each tl tiit flftlaifi fil with: the co 28*, 19241. Serial: No: 525,318.

ductor or antenna through individual three electrode vacuum tubes. The grid or control. element of. the tube of the receiving c rcuit isv given a normal, potential Within the operating range of the tube as a demodulator, the control element of the tube of the transl nitting circuit is given a normal potential. just outside of the operating range of this transmitting tubeWhen Working as an oscillator When the modue lating currents are applied, a portion of their energy is rectified and impressed on the control elements or grids of the two tubes. The effect of this is to make the grid of the receiving tube so negative as.- to

render that tube inoperative and to bring the grid of the tI'Elil-lSHl-lttllll-g tube: to such potential that this tube is in operative oscillating condition.

The nature of the invention will be better understood reference to the detailed description which follows, together with the drawing illustrating certainspecific circuits embodyin the invention, and in which Fig. 1. shows aduplex system embodying one form of the invention and Figs. 2. and 3 show modifications thereof. In each of the figures the various circuit elements are identified, as tar as possible, by reference characters suggestive of the function of the elements, parts identified by the same reference character being distinguished from each other different subscript numerals. Accordingly, the reference letters A, R, D, O, M, relate respectively to amplifiers, rectitiers, demodulators, oscillators and modulators. The elements Whichare common to the three systems and which are not a part of the present invention Will first be described, and this Will be followed by a detailed description of the improvements comprised in the present invention as applied to the three systems.

The common transmitting and receiving conductor 1 is illustrated; as an antenna, al though the principles of the invention are equally applicable to a carrier Wave system employing wires, in which case the common conductor would be the terminal circuit of the usual transmission line. Circuits at the left of the conductor 1 are receiving circuits, those at the right, transmission cir cuits. Referring to the receiving circuits,

electrode thermionic demodulating device is designated D. The structure of the tube and the arrangement of the circuits associated therewith may be varied from that shown according to the many diverse forms used in the art of demodulators generally. It will be understood, without further explanation, that the same generalization applies equally well to the circuits of the other thermionic devices. The indicating device 2 is associated, in the usual manner, with the output or the tube.

The transmitting circuits comprise, in the specific case illustrated, the low frequency modulating source 3, the high frequency carrier Wave source 0, and the modulator M. Although any other modulating system could equally well be used, in that selected for illustration the carrier and modulating waves are independently impressed on the filamentgrid circuit of an amplifying tube which functions to variably hmplity the carrier frequency current in accordance with the modulating wave. A. modulating current is supplied to the input circuit of the modulator from circuit through transformer 5. Although a circuit adapted for telephonic modulation has been disclosed, the principle and mode or operation of the invention does not exclude any other type of modulating means, whether involving a variation of the amplitude, or interruption of the modulating current. Although the low frequency indicating and modulating means associated respectively with the receiving and transmitting circuits are shown, for simplicity, as having no electric connection therebetween, it is obvious that they may be connected to a common transmitting circuit leading, for example, to a local tele phone exchange.

The transmitting circuits are normally in an inoperative condition, and must be put in an operative condition at the beginning of the normal modulating operation. The receiving circuits are normally in operative condition, and must be put into inoperative condition when the transmitting circuits are made operative. To accomplish this, the grid of the oscillator tube is normally given a sutiicient negative potential. to prevent the oscillator from functioning as such, but which will permit it upon response to a small positive increment of potential to become operative. The potential of the detector grid is critically adjusted in the reverse sense, so that a small negative'increment or potential will render the tube inoperative.

Reterring to Fig. 1, the grids of the demodulator and oscillator tubes are given their normal potentials in part by batteries 6 and 7, respectively, and in part by the potentiometer 8 which is associated with the rectifier R. The device B is denoted arec tifier to distinguish its function from that of demodulator D, although the internal action is essentially similar, i. e., the incoming current variations in the grid-filament circuit variably release energy in the plate tllament circuit. In the present case, the grid ofthe rectifier is operated over a range comprised below the knee oi the characteristic I E curve so that more energy is released during the positive halt cycle than during the negative half cycle. The grid filament circuit of the demodulator is so related to the potentiometer resistance and to the space current source 9, that the potential drop across that portion of the resistance between the terminals of the grid filament circuit normally adds aconstant negative potential to that contributed by the battery 6. Incom ing current variations derived from the circuit of microphone 3 by means of transformer secondary 10 set up rectified variations in the output circuit of the rectifier and add a sufficient negative potential to the grid of the demodulator to etfectually block the tube and render it inoperative. induction coil 13 functions to smooth out the variations in the circuit of which it forms a art-and therefore aids in the rectifying unction.

The grid-filament circuit of the oscillator, on the other hand, is connected to the potentio-meter resistance in a reverse sense so that'the potential normally impressed by the potentiometer on the grid of the oscillator is positive. This is opposed by a negative potential from battery 7, the adjustment or the respective potentials being such that the oscillator O is normally inoperative. The rectified variations from the microphone add a positive increment of sufiicient value to render the oscillator operative.

Accordingly the transmitting circuit is rendered operative and the receiving circuit inoperative.

' The arrangement comprising resistance 11 and condenser 12 associated with the grid battery 6 and the corresponding resistance 21 and condenser 22 associated with battery 7 prevents actuation of the system as above described except by a series of impulses sut iicien'tly prolonged as to have the character ist-ics of speech, and accordingly avoids the effects or extraneous variations 0t snort duration. The initial surge of current through resistance 11 or 21 will, flow through the condenser 12 or The potential across the condenser will accordingly be initially Zero and Will gradually build up as the condenser becomes charged. The time before which the difference of potential will be sufficient to effect the operation oi the devices D and 0 depends on the capacity of the con denser, which is made readily adjustable. This condenser will ordinarily have a re actance which is large compared with the The are

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1, scans-5 impedances of oscillation circuits associated with the oscillators.

The system of Fig. 2 dilfers from that of Fig. 1 only in means which permit the filaments of the two sets of tubes to be energized from a common source. An additional tube A between the rectifier and the oscillator is related to the rectifier output circuit in the same manner as the demodulator. The output circuit of this tube is like that of the rectifier except for the omission of the inductance 13, and is related to the oscillator in the same manner that the rectifier is related to the demodulator. When speech variations occur in the input of the rectifier, increasing its effective space current, the grid potential of tube A is accordingly decreased. This results in a de crease in current flow in the output circuit of tube A and, consequently, in an increase, or a smaller negative value, of the resultant potential on the oscillator grid. The arrangement indicated by reference numerals 11, 12 01 21, 22 may be placed in the input of the tube A or tube 0, as preferred, the former arrangement being here illustrated.

The system of Fig. 3 differs from that of Figs. 1 and 2 by a means providing a common space current source for the tubes. This means involves the use of .an additional tube, as compared with the system of Fig. 1, and the system may comprise also the distinctive features differentiating the system of Fig. 2 from that of Fig. 1, or separate filament energizing sources may be used, if desired. In Fig. 3, the space current source 9 is located adjacent to the filaments. The additional circuits necessary are sufiiciently obvious from the drawing to one conversant with the art, and will not be described here. The new arrangement of the battery 9, how ever, introduces certain changes in the mod-e of operation of the system and the adjust ment of some of the quantities which will be explained.

It is obvious that the reversal of the positions of the battery and potentiometer resistance as compared with Fig. 1, results in the addition of a normal positive potential on the grid of demodulator D to that contributed by the battery 6. Accordingly, in order to obtain the same resultant grid potential as before, the negative potential supplied by battery 6 must be greater than in the former case. Since the difference of potential between the filament and the point of connection of battery 6 can obviously never be greater than that of the battery 9, it is apparent that this difference in potential will decrease as the current in the resistance 8 increases. Accordingly, after adjustment has been properly made, the system as a whole functions in an identical manneras Fig. 1. The application of the changed conditions to the transmitting circuits will be obvious from consideration of the abovedescription and will not be discussed here. The system, except as has been pointed out, is the same as that of Fig. 2. In the claims, an increase in absolute value signifies a change toward, a positive or a more positive value. A change from a negative to a less negative value according ly represents an increase in absolute value.

The novel features inherent in the invention are defined in the appended claims.

VVhat is claimed is:

1. A signaling station comprising means for transmitting signals to a distanct point, cooperating means including a space discharge path for receiving and indicating signal energy transmitted from a distant point, and means controlledby signals to be transmitted and operating on said discharge path to render said receiving means inoperative during transmission while maintaining the condition of ionization of said path constant.

2. A carrier Wave transmission system comprising a transmitting circuit, a space discharge path in energy transfer relation therein and which is normally adjusted to have relatively high impedance, a receiving circuit, a space discharge path in energy transfer relation therein and which is normally' adjusted to have a relatively low impedance, a conductor operatively associated with both-the said circuits, and signal controlled means for substantially simultane.

ously rendering said high impedance relatively low and said lowimpedance relatively high.

3. A radio system comprising an antenna, transmitting apparatus which is normally inoperative electrically connected thereto, receiving apparatus which is normally operative also electrically connected thereto, each of said apparatuses including a space discharge path in energy transfer relation,

and signal controlled means operating on said paths for substantially simultaneously rendering said transmitting apparatus operative and said receiving apparatus inoperative Without changing the continuity of any of the circuits.

4:. A duplex signaling station comprising a transmitting conductor, a signal transmitting circuit and a signal receiving circuit electrically connected therewith, each including a space discharge path in energy transfer relation and signal responsive means for operating on said paths whereby the transmitting circuit is rendered operative and the receiving circuit inoperative Without varying the continuity of either of said circuits.

5. A duplex signal station comprising a transmitting 'COIIClLlCCOL'H signal transmit ting circuit electrically connected therewitlii art. including 'tln'eeelema. t thermionic peating device having a cathode, an anode and a control grid, a signal receiving circuit electrically connected with said conductor and containing a three-element thermionic repeating device having a cathode, an anode and a control grid, and signal responsive means whereby a blocking potential may be simultaneously impressed on the grid of the receiving device and removed from the grid of the transmitting device without varying the continuity of any of the circuits.

6. In combination, a transmitting conductor, a signal transmitting circuit electrically connected therewith including a thermionic oscillator having a cathode, an anode and a control grid, means for normally impressing a blocking potential on said grid, and means responsive to sound waves to be transmitted whereby said blocking potential may be effectively removed.

7. In combination, two circuits, each containing a three-element thermionic repeating tube including a control grid, and means whereby current in one of said circuits impresses a blocking potential on the grid of the tube in the other circuit and simultaneously effectively removes a blockingpotential from the grid of the tube in its own circuit.

8. A duplex modulated carrier wave transmission system comprising a transmitting conductor, a transmitting circuit and a receiving circuit electrically connected there with, and means whereby the modulating current renders said transmitting circuit operative and said receiving circuit inoperative without varying the continuity of any of the component circuit elements of either of said circuits.

9. In combination, a source of continuous electrical oscillations comprising an electric discharge device having a cathode, .an

anode, and a discharge controlling grid, means for modulating the output of said source according to signal variations, an electric discharge demodulating means comprising a cathode, an anode,and a discharge controlling grid, grid polarizing means in circuit between the grid and cathode of each of said discharge devices, a potentiometer source of electromotive force included in common in said grid cathode circuits, and means rcsponsiveto the signal variations for energizing said potentiometer source, the normal grid polarizing means being so adjusted that the demodu-v lating means is normally operative and the oscillating means is normally inoperative, and the grid cathode circuits of the said detecting and oscillating means being so connected to the potentiometer source, that the signal currents impressed thereon render the detecting means inoperative and the oscll- Iating means operative.

100 In a duplex radio telephone system in.

combination, an antenna, a transmitting and a receiving circuit operatively connected therewith, each of said circuits comprising an electric discharge device having a cathode, an anode, and a control grid, a rectifying means, means for impressing voice variations on the input of said rectifying means, an output circuit for said rectifying means including a resistance, circuit means connecting the filament and grid of each of said devices to two spaced points in said resistance, the connections being arranged oppositely with respect to the two devices, and a grid polarizing battery in the filament-grid circuit of each of said devices, the potential of said batteries and the connections to said resistance being adjusted so that rectified voice variations will render the device in the detector circuit inoperative and the device in the transmitting circuit operative.

11. The combination specified in claim 5, in which there is an inductance serially connected in the filament-grid circuit of each of said devices and a variable condenser shunted across each of said filament-grid circuits between the filament and the terminal of said inductance nearest the grid, whereby the time within which the said operations will be effected may be varied.

12. A duplex carrier wave telephone system comprising in combination a source of voice current, means for generating and transmitting a carrier wave modulated in accordance with said voice currents, and means for receiving and demodulating voice modulated carrier waves, potential biasing means in each of said means whereby the first mentioned means is normally inoperative and the second mentioned means is normally operative, a rectifier connected to said voice current source, and means operable under the influence of impressed voice currents whereby currents resulting from rectificationchange the biasing potentials in said means so as to make the first mentioned means operative and the second mentioned means inoperative.

13. A duplex radio telephone system comprising in combination a transmitting con ductor,'a receiving circuit connected therewith and including a three element thermionic repeating device having a cathode,

an anode and a control grid, and means normally impressing such a potential on said grid to render the anode-cathode circuit conductive, a transmitting circuit connected with said transmitting conductor and including a three element thermionic oscillator having a cathode, an anode and a control grid, and means for normally impressing such a potential on said control grid to render the anode-cathode circuit non-conductive, and voice operated means whereby thegrid potentials of the repeating device and of tn oscillator are respectivelgr creased and increased in absolute value so that the corresponding anode-cathode circuits are respectively non-conducting and effective to demodulate, Without varying the continuity of any of the circuits.

14. A carrier signaling set comprising transmitting apparatus including a high frequency oscillator circuit, a low frequency gnaling circuit associated therewith Whereby the high frequency oscillations may be modulated by the low frequency signals, a control circuit for said oscillator circuit, said control circuit including a resistance through which a predetermined potential drop exists, and a vacuum tube circuit controlled by said low frequency signaling circuit for varying the potential drop through said resistance to operate said control circuit.

15. A carrier signaling set comprising transmitting apparatus including a high fre-- quency oscillator circuit and a W frequency signalingcircuit associated therewith whereby the high frequency oscillations may be modulated by the low frequency signals, and receiving apparatus including demodulating means, a control circuit for said oscillator circuit, a control circuit for said demodulating means, said control circuits including a common resistance element through Which a potential drop exists, and a vacuum tube circuit controlled by said low frequency signaling circuit for varying the potential drop through said common resistance to operate said control circuits.

In Witness whereof, I hereunto subscribe my name this 24 day of December A. D,

H. TRAP FRIIS. 

